Positive displacement type fluid meter



Nv. 28, 1950 w. F. BERCK 2,531,603

` POSITIVE DISPLACEMENT TYPE FLUID METER Original Filed Sept. 17, 1945 6 Sheets-Sheet 1 INVENTOR. WILLIAM F'. BERCK ATTRNEYS Nov. 28, 1950 w F, BERCK 2,531,603

POSITIVE DISPLACEHENT TYPE FLUID METER Original Fld Sept. 17, 1945 6 Sheets-Sheet 2 Fiyi. o

Nov. 28, 1950 w. F. BERCK POSITIVE DTSPLACEEENT TYPE FLUTD METER Original Filed sept. 1'?, 1945 6 Sheets-Sheet 5 INVENTOR. WA4/.MM F. 5506/( Nov. 28, 1950 w. F. BERCK Original Filed Sept. 17, 1945 NVENTOR WILL/AM @ERC/f ATTORNEYS Nov. 28, 1950 w. F. BERCK 2,531,503

POSITIVE DISPLACEMENT TYPE FLUID METER Original Filed Sept. 17. 41945 6 Sheets-Sheet 5 /NvE/vron 3/ WILL/AM F. BERCK A T TORNEYS Nov. 28, 1950 w, F, BERCK 2,531,603

POSITIVE DISPLACEMENT TYPE FLUID METER Original Filed Sept. 17, 1945 6 Sheets-Sheet 6 @lf-.O 20 'Q 28 /v vE/v Ton WILL /AM F. @mmf B mammbmam A TTOR/VEVS atented Nov. 28, 1950 POSITIVE DISPLAIEMENT TYPE FLUID TER William F. Berck, Hayward, Calif., assignor to Ralph N. Brodie Company, Oakland. Calif., a corporation of California Continuation of application Serial No. 616,724,

September 17, 1945. This application Septembel 29, 1947, Serial N0. 776,756

. 9 Claims. 1

This invention relates to fluid meters.

This application is a, continuation of my application for Fluid Meter, Serial No. 616,724, led September 1'7, 1945, now abandoned.

It is the principal object of my present invention to provide an improved liquid meter of the positive displacement type which has substantially constant hydraulic characteristics and mechanical balance and which employs a pair ""of complemental meshing rotors operated by 21 pressure differential between the inlet and outlet sides of the meter to accurately and efficiently measure liquid passing through the meter with a, minimum of pressure drop.

v One form which the invention may assume is exemplified in the following description and illustrated by way of example in the accompanying drawings, in which:

Fig. 1 is a view in` central vertical section through a meter embodyingthe preferred form vof my invention.

Fig. 2 is a. view in elevation of the discharge end of the meter. Y.

Fig. 3 is a view of the interior face of one of the head members of the meter, showing the manner in which the inlet chamber is extended radially inward with respect to the rotors.

Fig. 4 is a view in plan, partially in section, through the meter taken on .line 4-4 of Fig. 2 and shifted through 180 in the plane of the paper, the inlet port having been superimposed in broken lines.

Fig. 5 is a view in longitudinal section taken along line 5-5 of Fig. 4.

Figs. 6 to 9, inclusive, are correlated diagrammatic views of the two rotors, showing the manner in which the liquid seal between the rotors is formed.

"Figs 10 to 12, inclusive, are diagrammatic views, showing the manner in which the trapped liquid is by-passed to the outlet chamber immediately as a socket changes from communication with the outlet port to communication with the inlet port.

Fig. 1.3 is an end view, showing the gear connectionbetween the rotors.

Fig. 14 is an inverted transverse sectional view through the meter taken on line I4-I4 of Fig. 4.

Referring more particularly to the accompanying drawings, IIJ indicates a meter of the displacement type. This meter comprises a primary meter casing II (hereinafter referred to as the meter casing) and an enclosing secondary casing I2. The latter houses auxiliary devices like, which form no part of the present invention. The secondary casing also 'constitutes a receiving medium for the fluid to be measured4 to feed the same to the inlet of the meter I0, and a medium for receiving the fluid passing from the outlet of the meter I0. Needless to say, the meter I0 is interposed in the casing I2 in a manner that the fluid delivered to the casing I2 must pass through the-meter I0 to discharge from the casing I2.

The meter casing II is formed interiorly with two cylinder bores I4 and I5, the axes of which are in parallelism. These cylinder bores I4 and I5 extend between the head members I6 and I1 of the meter casing II. The axialcenters of the lbores I4 and I5 are so spaced apart rela- 'tive to the diameters of the bores I4 and I5 that the latter intersect, forming a communieating opening I8 between the cylinder bores I4 and I5.

The cylinder bore I4 is of a diameter greater than the cylinder bore l5 as shown. The precise relationship of the diameters of the cylinder bores is, as will be described hereinafter, determined by the 'formation of complemental rotors I9I and 20 which are rotatably mounted therein.

The rotor 20 is fixed on a shaft 2I journalled v in bearings 22 carried by the head members I6 and I1. The rotor I9 is fixed on a shaft 23 journalled in bearings 24 carried by the head members I6 and I1. member I1, the shafts 2I and 23 are tted with meshing gears 24a to .cause opposite rotation of the rotors at predetermined relative speeds. Formed interiorly of the meter casing II exteriorly of the cylinder bores I4 and I-5 at one side thereof is an inlet chamber 25. This chamber 25 communicates with the interior of the bores I4 and I5 through inlet ports 26, which circumferentially overlie the said bores I4 and I5, and with the exterior of the casing through a circumferentially disposed port 21.

An -outlet chamber 28 is similarly formed in thefmeter casing at the opposite side of the cylinder bores I4 and I5 from the inlet chamber 25 and communicates with said bores I4 and I5 through a single outlet port 29. This outlet chamber 28 communicates with the exteriorv of the meter casing II through an axially disposed port 30 formed through the head member I6.

The ports 26 and 29 extend the entire length of the cylinder bores I4 and I5, but their side edges are contoured and located with relation to used in connection with gasoline meters and the the axial centers of the cylinder bores I4 and I5 Exteriorily of the head to enable precise timing of port opening and closing by the rotors I9 and 20 as will hereinafter be explained. The outer side edges of the ports 26 and 29 are formed along a helix line conforming to the helix angle of the lobes and sockets of the rotors I9 and 20, as shown in Fig. 4.

Intermediate the ports 26 is a longitudinal bridge member 26a which is merely a deflector to derive some benefit from directing the path of the iluid flow to the rotors. The side edges of the outlet port are similarly contoured for obvious reasons.

The inlet chamber has a portion 25a formed in the head member I1 and extending radially inward with respect to the rotors I9 and 20. The contour of the marginal edge of the inlet chamber portion 25a cooperates with the rotors, as will be described, to affect the time of inlet port opening and closing.

The port 30 in the head member I6 which communicates with the outlet chamber 28 is so located and contoured as to be complemental to the inlet chamber portion 25a and its marginal edges act to affect the time of outlet port opening and closing.

'I'he rotor I9 is formed with radially projecting and helically extending lobes 3l. These lobes 3| are provided with surfaces epicycloidal in crosslection transversely of their rotor axis and pro- `lect from a solid cylinder 33 whose external periphery is precisely at the root diameter of the lobes 3I. In this instance, the rotor I9 is formed with three lobes 3| equally spaced apart circumferentially.

The rotor 20 has an external diameter of such size that it will be in rolling contact with the periphery of the cylinder 33 at the root of the lobes 3|. The rotor 20 is formed with four helically extending lobe sockets 34 which are cornplemental to the lobes 3| on rotor I9 to mesh therewith. The lobe sockets 34 are provided with surfaces epitrochoidal in cross-section transversely. of their rotor axis. The peripheral speed of the rotor 20 is precisely that of the cylinder 33 at the root of the lobes 3I upon counter-rotation of the rotors due to the geared connection therebetween, as previously set forth.

The rotor 20 is formed with four lobe sockets in that I have determined that three lobes 3| on the rotor I9 and four sockets 34 in the rotor 20 is the most satisfactory from the standpoint of eillciency in operation.

I have determined that a ratio in which the rotor I9 has three teeth and the rotor 20 has four sockets enables a greater displacement per revolution of the rotor I9. By utilizing this ratio, it is possible to use a greater depth of tooth because the corresponding rotor is comparatively larger in diameter than it would be if a ratio of one to one was employed. For example, by employing a rotor 20 of a diameter of 2.250, the depth of the socket 34 is .714. The double depth of the socket 1.428 still leaves .822 base diameter. For this diameter 2.250 of the rotor 20, the diameter of the cylinder 33 of the rotor I9 would be 1.6875. If the design was for one to one ratio, the external diameter of the rotor 20 would be 1.6875. Subtracting the double depth of the socket 1.428 would leave .2595 as the base diameter of rotor 20 which would be too weak structurally.

I have also determined that employing e, ratio greater than three to four not only fails to result in an increase in displacement, but does prove objectionable in that it increases the weight and bulk of the rotor 20 and lessens the helix angle 4 of the teeth and sockets, which results in an actual loss in efficiency.

Another favorable result which is obtained by the use of a three to four ratio is that it results in a maximum of favorable turning moment of the rotors in operation. That is to say, the rotor 20 has a normal unfavorable turning moment and the rotor I9 has a normal favorable turning moment which is greater than the unfavorable turning moment of the rotor 20 so that in operation energy from the favorable turning moment of the rotor I9 must be utilized to rotate the rotor 20. Thus the three to four ratio causes the rotor I9 to travel faster than the rotor 20 and results in greater efliciency.

I have determined the maximum permissible lhelix angle of each tooth of the rotor I9 which is the most e'iiicient, this maximum being such that the angle between two lobes plus the angle of circumferential advance of one tooth in the length of the rotor is not greater than the angle traversed by the rotor throughout its cyinder bore between the points of intersection with the other cylinder bore. lThis maximum helix angle at the outside diameter of the rotor I9 is approximately 52. 'Ihe length of the rotor bears a definite relationship to the lead of the tooth, which relation can be expressed as 1ength 1 lead 2.25

This is the maximum helix angle which will allow one complete tooth of rotor I9 to be in contact with the wall of the cylinder bore for effecting a seal and subject to differential pressure at all times.

It should be pointed out that the relative crosssectional formation of the lobes 3| and sockets 34 is such that at all times there is a longitudinal sealing contact between the rotors throughout the full length thereof. Such a seal is effected by contact of a lobe edge 3Ia (which is slightly flattened) with a socket surface 34b, by contact of one or both edges 34a of the socket surfaces with the lobe faces 3Ib, and by contact between the periphery of the rotor 20 between the sockets 34 and the periphery of the cylinder 33 between the lobes 3 I.

This seal is diagrammatically illustrated in Figs. 6 to 9, inclusive, in which the rotor I9 is illustrated as rotated ninety degrees clockwise from starting position and rotor 20 is illustrated as rotated ninety degrees counterclockwise from starting position. These arbitrary positions of the rotors were chosen fcr illustration because the line of sealing effected by the cooperating faces of the rotors can be best illustrated by such rotor positions.

Referring to these figures, it is seen that in proper mesh the edge B at the terminal of one socket of rotor 20 would contact with the rotor I9 at B' which is at the intersection of the lobe and cylinder 33 of rotor I9. 'Ihis edge B extends along one face of the lobe in sealing contact therewith longitudinally of the lobe and radially outward until the line of contact intersects the outer lobe edge A at C. This lobe edge A is in sealingcontact with the socket surface from the' point C to the point A. Thus a sealing contact is made along a seal line extending from the point C longitudinally and radially outward to the point A at the terminal of the opposite edge of the socket. The sealing line of contact is then formed by engagement of the last named socket edge with the lobe face along a line extending longitudinally and radially inward from A' to D which vis at the root of the lobe. At this point the periphery of the rotor 20 is in line sealingcontact withthe periphery of the cylinder of the rotorvls from D to E. From this point a sealing line of contact is formed between the socket edge and the face of the lobe which extends longitudinally and radially 'outward from E to F at the rotor end. The end of the socket is'sealed by the end oi' the cylinder from F to G. Thence a line of sealingcontact is made by contact bey tween the socket edge and the lobe face from G to H.v A sealing contact is also made between the lobe edge from H to F2 and the socket surface from H to F1, as indicated.

The seal linejust described, of course, constantly varies during the operation of the rotors due tothe helical disposition of the lobes 3| and lobe sockets 34 and the cross-sectional shape thereof. However, the dispositionA of that seal between the rotors I9 and 20 and the seal lines between the outer peripheries of the rotors and the cylinder walls, taken in conjunction with the helical angle of the lobes 3| and'lobe sockets 34,

so disposes the surfaces of the lobes 3| and lobe sockets 34 to the inlet and outlet pressures that the differential between those two pressures results in rotation of the rotor I9 in the correct direction (clockwise in the arrangement depicted in Fig. 14), and rotor 2li in the incorrect direction (counterclockwise in the arrangement depicted in Fig. 14), with a resultant rotation of both rotors in the correct direction for any given pressure differential. The ratio between the resultant force tending-to rotate the rotors I9 and I;

20 in the correct direction upon the creation of a pressure differential between the inlet and outlet sides of the rotors I9 and 20 and the forces resisting such rotation is of the order of four to one.

It is desired to point out here that the formation of the rotors I9 and 20 and their lobes 3| and lobe sockets 34, which causes them to rotate 6 For this reason passageways d are formed in the end face of each lobe which communicate with the leading face of the lobe and then extend radially inward so that they will be in communil way from the outlet chamber.

At the opposite end of the casing Il, the seal line of the portion 25a of the inlet chamber is precisely in register with the seal line of the port 30 of the outlet end chamber. At this end the lobes 3| are formed with passageway d' similar to the passageways d except that they extend through the trailing edge of the lobe 3| and act to prevent an attempt to draw a partial vacuum between a lobe 3| and its socket as it changes from communication with the inlet chamber or port to communication with the outlet chamber or port. A

In operation of the meter, it is constructed and assembled as shown in the drawings, and, of course, inlet fluid under pressure is directed to the inlet chamber. The outlet chamber is in communication with the discharge line, preferably connected to the secondary casing I2. Ob-

with substantially constant torque for any given pressure differential, results in a meter having substantially constant hydraulic characteristics..

Just prior to a lobe 3| completely traversing a' lobe socket 34 and displacingl the liquid therefrom endwise into` the outlet chamber, an end seal must be effected to'prevent communication between the inlet and outlet chambers through that socket. In Figs. 10 to-1'2, inclusive, a lobe 3| is shown at this point and it is seen that a pocket of outlet liquid a is disposed between one face of the lobe 3| land the socket 34. As the lobe 3| continues to advance, a pocket b is formed between the opposite face of the lobe 3| and the socket 34, which pocket b will be' in communica- A tion with the inlet chamber'while thepocket a,

which is gradually diminishing,v will be in communication with the outlet chamber. Obviously, it is necessary that a seal be eifected'to'` prevent inlet liquid from by-passing axially through the socket through the pocket 'b into the outlet. For this reason the contour of the port 30 at the end of the outlet chamber is formed to effect anyend` seal. The seal line of the port 30y of the outlet chamber is shown in Fig. 2 at c and will effect a 'n seal over the socket 34 when it arrives atl the position shownlin Fig. 10. It is seen that this seal line c is such that it completely seals in the socket when lit arrives in the position shown in Fig. 10,

but at this time it is necessary, in order to prevent an attempt at compression of theliquidin pocket a, that this pocket communicate with the outlet chamber.

vunits of measure by a proper counter.

viously, there will be a pressure differential between the inlet and outlet uid. which pressure differential need not be very great because my present meter will operate under a small pressure differential in favor of the inlet side. The helix angle of the lobes 3| and sockets 34 and the contours of the inlet and outlet ports are such that the fluid pressure differential will so exert itself on the faces of the lobes and sockets as to cause the rotors I9 and to rotate in a metering direction. As the sockets open to the inlet ports 26, they will be lled with fluid, and when they commence to mesh with a complementary lobe, the latter will progressively and axially displace the liquid in the socket and discharge the liquid into the outlet chamber without at any time enabling communication to be established between the inlet and outlet chambers.

Immediately as the socket changes from communication with the outlet chamber to communication with the inlet chamber, it is sealed from the outlet chamber and the small amount of trapped uid will by-pass through the passageways d into the outlet chamber, as described. Likewise, as the sockets change from communication with the inlet chamber to communication with the outlet chamber, the end of the socket is likewise sealed off, but communication between the isolated space between the socket and lobe remains in communication with the inlet chamber. as described.

The rotor 20 is geared to a counter drive transmission 50, as shown in Fig. `2, in order that the liquid passed through and measured by the meter will be translated into gallons or other Inasmuch as the counter does not form any part of my present invention, it is not illustrated.

Formulae are given below for designing the pertinent elements of an actual meter in accordance with the present invention, which em- A=1ead 3T (3 tooth) rotor=estimate B=O. D. 3T rotor:A/2.1666

:root diam. 3T rotor=B .5-i16 D=O. D. 4T (4 tooth) rotor=4/3 C E=center distance=C+D/2 F=1ength oi' rotors:A/2

H:lead 4T rotor:4/3A J =R. P. M. 4T rotor:G. P. M./G1 (in gal.)

K =ve1ocity thru meter n F. P. S.=

L=R P. S. 4T rotor=J/60 M:R. P. S. 3T rotor:4/3 XL N=rev. per gal. of 3T rotor:231/G2 y :junction of helix angles in body=F .0625

or 1/ 36 XA Using the above formulae, specications of an actual meter are given herewith, based upon helical epicycloidal teeth and epitrochoidal sockets, the 3 tooth rotor I9 having a helix angle of 55` A=lead 3T rotor:l0.0

B=O. D. 3T rotor=4.6l5

C':R. D. 3T rotor:2.500

B=O. D. 4T rotor=3.333

E=center distance:2.9166

F=length:5.0"

G1=displacement per one rev 4T rotor:76.14 in.3

(with 1% included for s1ippage:76.9 in?) G2=displacement per one rev 3T rotor=57.67 in.3

(with 1% included for slippage) H:lead 4T rotor:13.333

J :R. P. M. 4T rotor:@ 150 G. P. M.:450 R. P. M. 200 G. P. M. 600 R. P. M. 250 G. P. M.=750 R. P. M. :velocity thru meter=@ 150 G. P. M.:7 F. P. S. 200 G. P. M.:9 F. P. S. 250 G. P. M.=12 F. P. S.

L:rev. 4T rotor in R. P. S.=@ 150 G. P. M.:

7.5 R. P. S.

8 f Having thus described my invention, what il claim and desire to secure by Letters Patent is:

1. A positive displacement liquid meter comprising a casing having a pair of parallel intersecting cylindrical bores, inlet chamber lformed therein exteriorly of one side of the bores and an outlet chamber exteriorly oi' the other side of the bores. said casing M=rev. 3T rotor in R. P. S.=@ 150 G. P. M.:

10.0 R. P. S. N=rev. 3T rotor per gallon:4.0055 P=junction of helix:.281

From the foregoing it is obvious that I have provided a very eillcient positive displacement liquid meter which will accurately and eillciently lskilled in the art without departing from the spirit of the invention as dened in the appended claims.

having an inlet port between the inlet chamber and the bores and an outlet port between the outlet chamber and the bores, a ilrst rotor rota-- tably mounted in one bore, a second rotor'rotatably mounted in the other bore, the rst rotor having at least three radially projecting helically extending lobes having surfaces epicycloidal in cross-section transversely of their rotor axis and of an outer diameter sealingly fitting the bore, the second rotor having a diameter sealingly fitting its bore and engaging the periphery of the ilrst rotor vat the root oi' the lobes, a connection between the rotors whereby they will rotate in counterdirections with the peripheral speed of the second rotor` being equal to theperipheral speed of the ilrstrotor at the root vof the lobes. the second rotor having at least four helically extending sockets having surfaces epitrochoidal in cross-section transversely of their rotor axis and complemental to the lobes to mesh therewith to form a constant liquid seal longitudinally between the rotors and thereby between the inlet and outlet ports. said inlet port extending on opposite sides oi' the line of intersection between the outer diameters oi.' the rotors and the entire length of the rotors and having oppositely converging helical side edges one conforming to the helix angle of the sockets and the other to the helix angle of the lobes and intersecting at one end of the rotors at the point of intersection of the outer diameters of the rotors, said outlet port being formed similarly to the inlet port but with its helical side edges intersecting atthe point of intersection of the outer diameters of the rotors at the opposite end of the rotors.

2. A positive displacement liquid meter comr prising a casing having-a pair of parallel intersecting cylindrical bores, said casing having an inlet chamber formed therein exteriorly of one side of the bores and an outlet chamber exteriorly of the other side of said bores, said casing having an inlet port between the inlet chamber and the bores and an outlet port between the outlet chamber and the bores, a, rst rotor rotatably mounted in one bore. a second rotor rotatably mounted in the other bore, the rst rotor having at least three equally circumferentialiy spaced radially projecting helically extending lobes having surfaces epicycloidal in cross-section transversely of their rotor axis and of an outer diameter sealingly fitting the bore, the second rotor having a diameter sealingly tting its bore and engaging the periphery of the rst rotor at the root of the lobes, a gear connection between said rotors whereby the peripheral speed of the second rotor will be the same as the peripheral speed of the rst rotor at the root of the lobes, the second rotor having at least four helically extending sockets having surfaces epitrochoidal in crosssection transversely of their rotor axis and com- `plemental to the lobes to mesh therewith to form a constant liquid seal longitudinally between the rotors and thereby between the inlet and outlet chambers, the angle between two lobes plus the angle of circumferential advance of vone tooth in the length of the rotor not exceeding the angle traversed by the ilrst rotor throughout said casing having'an its cylinder bore between the points of intersection with the other cylinder. said inlet port extending on opposite sides of the line of intersection between` the outer diameters of the rotors and the entire length of the rotors and having oppositely converging helical side edges one conforming to the helix angle of the sockets and the other to the helix angle of the lobes and intersecting at one end of the rotors at the point of intersection, of the outer diameters of the rotors, said outlet port being formed similarly to the inlet port but with its helical side edges intersecting at the point of intersection of the outer diameters of the rotors at the opposite end of the rotors.

3. A positive displacement liquid meter comprising a casing having a pair of parallel intersecting cylindrical bores, said casing having an inlet chamber formed therein exteriorly of one side of the bores and an outlet chamber exteriorly of the other side of the bores, said casing having an inlet port between the inlet chamber and the bores and an outlet port between the outlet chamber and the bores, a. flrst rotor rotatably mounted in one bore, a second rotor rotatably mounted in the other bore, the rst rotor having at least three radially projecting helically extending lobes having surfaces epicycloidal in cross-section transversely of their rotor axis and of an outer diameter sealingly fitting the bore, the second rotor being of a diameter sealingly fitting its bore and engaging the periphery of the rst rotor at the root of the lobes, a connection between the rotors whereby they will rotate in counterdirections with the peripheral speed of the second rotor being equal to the peripheral speed of the iilfst rotor at the root of the lobes, the second rotor having at least four helically extending sockets having surfaces epitrochoidal in cross-section transversely of their rotor axis and complemental to the lobes to mesh therewith to form a constant liquid seal longitudinally between the rotors and thereby between the inlet and outlet ports, the angle between two lobes plus the angle of circumferential advance of one tooth in the length of the rotor not exceeding the angle traversed by the rst rotor throughout its cylinder bore between the points of intersection with the other cylinder, said inlet port extending on opposite sides of the line of intersection between the outer diameters of the rotors and the entire length of the rotors and having oppositely converging helical side edges one conforming to the helix angle of the sockets and the other to the helix angle of the lobes and intersecting at one end of the rotors at the point of intersection of the outer diameters of the rotors, said outlet port being formed similarly to the inlet port but with its helical side edges intersecting at the point of intersection of the outer diameters of the rotors at the opposite end of the rotors, passage means for conducting liquid trapped between a lobe and a socket to the outlet chamber immediately as the socket changes from communication with the outlet chamber to communication with the inlet chamber without establishing a communication between the inlet and outlet ports.

4. A positive displacement liquid meter comprising a casing having a pair of parallel intersecting cylindrical bores, said casing having an inlet chamber formed therein exteriorly of one side of the bores and an outlet chamber exteriorly of the other side of the bores, said casing having an inlet port between the inlet chamber and the bores and an outlet port between the outlet chamber and the bores, a. first rotor rotatably mounted in one Abore..a second rotor rotatably mounted in the other bore,` the first rotor having at least three radially projecting helically extending lobes having surfaces epicycloidal in cross-section transversely of their rotor axis and of an outer diameter sealingly fitting the bore, the-second rotor being of a diameter sealingly fitting its bore and engaging the periphery of the first rotor at the root of the lobes, a, connection between the rotors whereby they will rotate in counterdirections with the peripheral speed of the second rotor being equal to the peripheral speed of the first rotor at the root of the lobes, the second rotor having at least four helically extending sockets having surfaces epitrochoidal in crosssection transversely of their rotor axis and complemental to the lobes to mesh therewith to form a constant liquid seal longitudinally between the rotors and thereby between the inlet and outlet ports, the angle between two lobes plus the angle of circumferential advance of one tooth in the length of the rotor not exceeding the angle traversed by the first rotor throughout its cylinder bore between the points of intersection with the other cylinder, said inlet port extending on opposite sides of the line of intersection between the outer diameters of the rotors`and the entire length of the rotors and having oppositely converging helical side edges one conforming to the helix angle of the sockets and the other to the helix angle of the lobes and intersecting at one end of the rotors at the point of intersection of the outer diameters of the rotors, said outlet port being formed similarly to the inlet port but with its helical side edges intersecting at the point of intersection of the outer diameters of the rotors at the opposite end of the rotors, passage means for conducting liquid trapped between a lobe and a-socket to the outlet chamber immediately as the socket changes from communication with the outlet chamber to communication with the inlet chamber without estab.- lishing a communication between the inlet and outlet ports, and passage means for conducting fluid from the inlet port to between a lobe and a socket as a socket changes from communication with the inlet port to communication with the outlet port to prevent drawing a partial vacuum and without establishing communication between the inlet and outlet ports.

5. A positive displacement liquid meter comprising a casing havinga pair of parallel intersecting cylindrical bores, said casing having an inletchamber formed therein exteriorly of one side ofithe bores and an outlet chamber exteriorly of the other side ofthe bores, said casing having an inlet port between the inlet chamber and the bores and an outlet port between the outlet cham ber and the bores, a rst rotor lrotatably mounted in one bore, a second rotor rotatably mounted in the other bore, the first rotor having three radially projecting helically extending lobes having surfaces epicycloidal in cross-section transversely of their rotor axis and of an outer diameter sealingly fitting the bore, the second rotor having a diameter sealingly fitting its bore and engaging the periphery of the first rotor at the root of the lobes, a connection between the rotors whereby they will rotate in counterdirections with the peripheral speed of the second rotor being equal to the peripheral speed of the first rotor at the root of the lobes, the second rotor having four helically extending sockets having surfaces epi- 4 trochoidal in cross-section transversely of their rotor axis and complemental to the lobes to mesh therewith to form a constant liquid seal longitudinally between theA rotors and thereby between the inlet and outletports, said inlet port extending on opposite sides of the line of intersection between the outer diameters of the rotors and substantially the entire length of the rotors and having oppositely converging helical side edges one conforming to the helix angle of the sockets and the other to the helix angle of the lobes and intersecting at one end of the rotors at the point of intersection of the outer diameters of the rotors, said outlet port being formed similarly to the inlet port but with its helical side edges intersecting at the point of intersection of the outer diameters of the rotors at the opposite end of the rotors.

6. A positive displacement liquid meter comprising a, casing having a pair of parallel intersecting cylindrical bores, said casinghaving an inlet chamber formed therein exteriorly of one side of the bores and an outlet chamber exteriorly of the other side of the bores, said casing having an inlet port between the inlet chamber and the bores and an outlet port between the outlet chamber and the bores, a first rotor rotatably mounted in one bore, a second rotor rotatably mounted in the other bore, the first rotor having three radially projecting helically extending lobes having surfaces epicycloidal in cross-section transversely of their rotor axis and of an outer diameter sealingly fitting the bore, the second rotor being of a diameter sealingly fitting its bore and engaging the periphery of the first rotor at the root of the lobes, a connection between the rotors whereby they will rotate in counterdirections with the peripheral speed of the second rotor being equal to the peripheral speed of the first rotor at the root of the lobes, the second rotor having four helically extending sockets having surfaces epitrochoidal in cross-section transversely of their rotor axis and complemental to the lobes to mesh therewith to form a constant liquid seal longitudinally between the rotors and thereby between the inlet and outlet ports, the angle between two lobes plus the angle of circumferential advance of one tooth in the length of the rotor not exceeding the angle traversed by the first rotor throughout its cylinder bore between the points of intersection with the other cylinder, said inlet port extending on opposite sides of the line of intersection between the outer diameters of the rotors and the entire length of the rotors and having oppositely converging helical side edges one conforming to the helix angle of the sockets and the other to the helix angle of the lobes and intersecting at one end of the rotors at the point of intersection of the outer diameters of the rotors, said outlet port being formed similarly to the inlet port but with its helical side edges intersecting at the point of intersection of the outer diameters of the rotors at the opposite end of the rotors, passage means for conducting liquid trapped between a lobe and a socket to the outlet chamber immediately as the socket changes from communication with the outlet chamber to communication with the inlet chamber without establishing a communication between the inlet and outlet ports, and passage means for conducting fluid from the inlet port to between a lobe and a socket as a socket changes from communication with the inlet port to communication with the outlet port to prevent draw- 12 ing a partial vacuum and without establishing communication between the inlet and outlet ports.

7. A positive displacement liquid meter such as defined in claim l wherein the ends 'of said casing are provided with outwardly extending pockets overlying the intermeshing portions of said rotors, and wherein the lobes of said first rotor are provided at one end thereof with channels extending through the leading faces thereof and wherein said lobes are provided at their opposite ends with channels extending through the trailing faces thereof.

8. A positive displacement liquid meter of the character described comprising first and second casing head members; a first rotor journaled in said casing head members and provided with four helical lobes defining intermediate helical sockets of trochoidal configuration; a second rotor journaled in said casing heads and provided with three helical lobes of epicycloidal configuration meshing and forming a liquid seal with the lobes of said first rotor; a first casing side portion overlying said first rotor and formed on a radius substantially equal to the radius of said first rotor, said side portion being bounded by helical side edges in substantial parallelism with the lobes ot said first rotor and extending substantially throughout the length of said rotor, said side edges subtending an angle at least as great as the angle subtended by two adjacent lobes of said first rotor; a second casing side portion overlying said second rotor diametrically opposite said first casing side portion and formed on a radius substantially equal to the radius of said second rotor, said second casing side portion being bounded by helical side edges in substantial parallelism with the lobes of said second rotor and extending substantially throughout the length thereof, said side edges subtending an angle at least as great as the angle subtended by two adjacent lobes of said second rotor; liquid delivery and discharge charnbers merging with the said side edges of said first and second casing side portions; and means responsive to the rotation of one of said rotors for rotating the other of said rotors.

9. A positive displacement liquid meter of the character defined in claim 8 wherein said casing head members are provided with outwardly extending pockets overlying said discharge chamber andextending over the meshing zone of said rotors, and wherein the lobe faces of said second rotor are provided at one end of said rotor with channels extending through the leading faces of said lobes and at their opposite ends with channels extending through the leading faces thereof.

WILLIAM F. BERCK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,243,874 Lysholm June-3, 1941 2,287,716 Whitfield June 23, 1942 2,325,617 Lysholm Aug. 3, 1943 2,441,771 Lysholm May 18, 1948 FOREIGN PATENTS Number Country Date 528,678 France Aug. 23, 1921 

